Without limiting the scope of the present disclosure, its background is described in connection with external fixation devices. Generally, external fixation devices are commonly used on both the upper and lower limbs for both adults and children in a variety of surgical procedures including limb lengthening, deformity correction and treatment of fractures, mal-unions, non-unions and bone defects.
One common external fixation device is known as the Ilizarov Apparatus. The Ilizarov external fixation procedure involves a rigid framework consisting of several rings or arches that are placed externally around the limb and attached to injured (e.g., due to fracture) or surgically separated (e.g., for limb lengthening and deformity correction) bone segments using special bone fasteners (wires and pins) inserted into the bone segment and connected to the related section of the external rigid framework. The opposite rings of the rigid framework are connected by either threaded or telescopic connection rods or by assembled uni-planar or multi-planar angular hinges, which allow the surgeon to adjust the relative position of the rings to each other longitudinally or angularly over a period of time. This allows new bone to gradually form in the gap between bone segments created by this distraction technique. Once the desired position of bone segments is achieved over the course of time (e.g., 2-6 weeks), the external apparatus is stabilized into a fixed position and left on the bone segments until the fracture is healed or newly formed bone is completely or substantially mineralized, which could take up to an additional 3-6 months, depending on the nature of pathology and degree of deformity.
Another common external fixation device is a Taylor Spatial Frame as described in U.S. Pat. Nos. 6,030,386, 5,891,143, and 5,776,132. The Taylor Spatial Frame is a hexapod type of device based on a Stewart platform but shares many components and features of the Ilizarov apparatus. The Taylor Spatial Frame consists of two external fixator rings attached to bone segments by wires or half pins and connected together by 6 struts that may be lengthened or shortened as necessary. Adjustment of strut lengths allows manipulation of the bone segments in 6 axes (e.g., lengthening/shortening, external/internal rotation, anterior/posterior horizontal translation, medial/lateral horizontal translation, anterior/posterior angular translation, and medial/lateral angular translation) to correct linear, angular and rotational deformities simultaneously. The rings of the device include apertures or holes for attachment of wires and half pins and positioning of the struts and other connection elements. However, there are a finite number of holes on each ring, six of which are occupied with struts. This creates a positioning problem for wire and half pin attachment and placement of the additional connection rods due to the competition for holes in the ring.
In addition, the configuration of the rings of the Taylor Spatial Frame requires the struts to be connected at the top or bottom of the rings. To provide such connections, the rings are configured to receive only either ball joints in the holes of the rings or universal joints extending from the top or bottom surfaces of the rings. Both types of joints, however, have drawbacks. One drawback for using rings that are coupled to ball joints is that there is insufficient spatial clearance for the ball joints to effect some adjustments to the orientation of the struts and the rings. A drawback for using rings coupled to universal joints is the decrease in the functional length of the struts due to the space taken up by the length of the universal joints. Another drawback is the instability caused by universal joints. The universal joints each include at least one hinge connection, in which a pivot pin is commonly and loosely held by two rotating parts that are designed to rotate about the longitudinal axis defined by the pivoting pin. Due to the loose coupling between the rotating parts and the pivoting pin, a degree of undesirable translational movement is inherent in the design of the hinge connection and introduces instability to the Taylor Spatial Frame. Accordingly, the requirement of attaching the struts at the top or bottom of the rings ultimately leads to instability and limited range of motion in the Taylor Spatial Frame.